Wet spinning process of an elastomeric polymer thread

ABSTRACT

The present invention relates to a wet spinning process of an elastomeric polymer thread comprising a wet spinning phase in which a spun prepolymer is passed in equicurrent to a reactive solution to give a polymeric thread, a drying phase in which the solvent of the reactive solution is removed from the yarn and a collection phase in which said thread is wound on winding devices.

[0001] The present invention relates to a wet spinning process of an elastomeric polymer thread.

[0002] In particular, the present invention relates to a process for the wet spinning of an elastic polyurethane thread which comprises a reactive bath of the dynamic type.

[0003] As elastomeric polymers, in particular polyurethane elastomers, in the form of fibres, are widely applied in the textile industry, they are arousing growing interest from a commercial point of view.

[0004] A particular elastomeric polymer in the form of a fibre, spandex, is a well-known component which is widely used in the clothing industry, in particular for the production of items for sportswear or for increasing the elasticity of garments. The term spandex, commonly used for indicating elastomers, refers, by definition, to a synthetic polymer based on polyurethane, containing structurally rigid regions alternating with structurally elastic regions within a polymeric structure.

[0005] From a general point of view, three processes are currently known for the production of fibres from polyurethane polymers: dry spinning, wet spinning and melt spinning.

[0006] It is known that spandex is mainly spun with a dry or wet method, as melt spinning is still not capable of providing a sufficiently high-quality product for the present uses.

[0007] In the dry method, a viscous solution of a polymer in a suitable organic solvent, such as dimethyl formamide (DMF) or dimethyl acetamide (DMAC) is sent to dies situated at the top of a column where there is a flow of hot nitrogen or air. At the outlet of the dies, the threads descend inside the column for collection, near the bottom of the column, whereas the gaseous stream causes the evaporation of the solvent which is then condensed and recovered.

[0008] This process is advantageous for the production of threads with a low or medium titer. For the production of threads with a medium or high titer, on the contrary, the wet spinning process is generally used.

[0009] This process comprises two types of variations: the coagulation method and reactive bath method.

[0010] In the first method, a viscous solution of polymer in a suitable solvent (DMF or DMAC) is sent to the dies which are situated inside a coagulation bath normally consisting of a mixture of water and the solvent itself.

[0011] The residual solvent impregnated in the threads is subsequently removed from the threads generally by means of washing with water, by passage through one or more tanks positioned in sequence. The threads are finally dried and collected.

[0012] In the second method, the reactive bath method, the starting material to be subjected to spinning is different: this is a mass prepolymer, i.e. without solvent, in the form of a viscous fluid. This prepolymer is sent to the dies which are situated in a bath containing a reactive substance, belonging to the group of diamines, capable of reacting very rapidly with the prepolymer to give a polymer. Inside the reactive bath, the reactive substance (diamine) is diluted in an organic solvent in which however the polymer produced is insoluble. At the outlet of the tank, the threads, now consisting of polymer, are still impregnated with solvent which is removed by evaporation. For this purpose, the threads are transferred, by means of a conveyor belt or series of rolls, inside a passage-oven. The dried threads are finally collected by means of conventional winding devices.

[0013] An aspect which is common to both types of wet process is that the different baths through which the threads pass, whether they be coagulation, washing or reactive baths, are substantially of the static type. This means that they are contained in static baths which are not subjected to any stirring, in which the only movement of the liquid contained therein consists of its slow but continuous exchange through a fill-up and overflow.

[0014] The wet spinning processes of the known type, however, have their disadvantages for use, mainly attributed to the reduced spinning rate which thus causes a low production yield.

[0015] Furthermore, it has been observed in the conventional wet spinning techniques, that the occasional breakage of a spandex filament also jeopardizes the spinning of the adjacent threads, thus reducing the final production yield.

[0016] This problem is particularly serious in processes in which the threads of the production line run parallel and very close to each other in a common tank. In this case, the interference created by the breakage of a thread can negatively influence many of the adjacent threads.

[0017] In the present state of the art, the necessity has therefore been felt for a new process for the spinning of spandex which is highly efficient and allows optimized yields and production costs.

[0018] One of the general objectives of the present invention therefore consists in providing a spinning process of an elastomeric polymeric thread with the reactive bath wet method, which allows the disadvantages found in the known art to be avoided or substantially limited.

[0019] A further objective of the present invention consists in providing a process for the production of spandex threads which allows a particularly fast and efficient spinning.

[0020] Yet another objective of the present invention consists in providing a process for the wet spinning of polyurethane threads which requires equipment with reduced dimensions.

[0021] In view of these objectives and others which will become apparent from the following description, a wet spinning process is provided, in accordance with a first aspect of the present invention, of an elastomeric polymer, which includes:

[0022] a wet spinning phase in which a prepolymer is put in contact with a reactive solution to give a polymeric thread;

[0023] a drying phase preferably heated, in which the solvent of the reactive solution is removed from the thread;

[0024] a collection phase in which said thread is wound on winding devices;

[0025] said process being characterized in that in the wet spinning phase, said reactive solution moves in the direction of the thread-run in order to considerably reduce the hydrodynamic friction between the thread and reactive bath.

[0026] It has been found that by effecting the spinning of a polymer in the presence of a flow of reactive solution which moves in equicurrent with the thread, the hydrodynamic friction between the thread and reactive bath is substantially reduced, causing a consequent increase in the spinning rate. During the wet spinning phase, said reactive solution preferably moves inside a running device, at a rate preferably ranging from 15 to 80 m/min., more preferably from 30 to 60 m/min.

[0027] In accordance with a preferred embodiment, the process of the invention comprises:

[0028] feeding a prepolymer in mass to a spinning line comprising a series of spinning positions, each equipped with an independent reactive bath based on a reactive solution;

[0029] spinning a prepolymer in mass in the presence of a flow of said reactive solution which moves in equicurrent with the direction of the yarn-run;

[0030] winding the thread onto bobbins, after applying a layer of finishing oil to the surface of said polymer.

[0031] The term reactive solution refers to a mixture of a substance which reacts with the prepolymer promoting its partial or total polymerization. The reaction solution conveniently comprises a reagent substance dissolved in a solvent which however does not have a solvent capacity with respect to the polymer produced. According to an embodiment of the invention, said reactive substance belongs to the group of diamines, capable of rapidly transforming the prepolymer into a polymer, such as ethylenediamine, for example. A typical reactive solution is a mixture of toluene and ethylenediamine (EDA), with an EDA content preferably ranging from 4-6% by weight.

[0032] The term prepolymer in mass indicates a prepolymer in the form of a viscous fluid, without solvent. Examples which can be mentioned are prepolymers belonging to the group of polyester-urethanes, polyether urethanes or mixtures such as polyether/polyester-urethanes.

[0033] The reaction between the urethane prepolymer and diamine leads to the formation of chemical bonds of the ureic type; molecules of polymer are thus formed, by means of a prepolymer chain extension mechanism.

[0034] The method of the invention is particularly suitable for the production of polyurethane elastomers of the spandex type.

[0035] The characteristics and advantages of an embodiment of the process according to the present invention will become more evident from the following illustrative but non-limiting description, referring to the schematic drawings enclosed, wherein:

[0036]FIG. 1 shows a flow diagram of an embodiment of the process of the invention;

[0037]FIG. 2 illustrates a schematic side view of a spinning position, used for effecting the process of the invention in which the dies are shown in an operating position, situated inside a reactive bath and in rest position;

[0038]FIG. 3 shows a schematic plan view from above of the spinning position, according to FIG. 2.

[0039] With reference to FIG. 1, this illustrates a spinning line 1 for effecting an embodiment of the process of the invention. The prepolymer is fed through a feeding line or collector 2 to a spinning pump 3 which moves it through a filter 4 to reach a spinning section 6. The latter is equipped with one or more dies (not shown) immersed in a reactive bath based on a reactive solution capable of polymerizing the prepolymer.

[0040] In the spinning section 6 the prepolymer is spun in threads which pass through a reactive bath, subsequently moving through and inside a transporting device in equicurrent with the stream of reactive solution coming from the bath itself. This transporting device advantageously comprises a horizontal tube 7 slightly inclined downwards. The thread comes into contact with the reactive solution in the reactive bath and while running inside said horizontal tube, wherein the thread runs in the same direction as the reactive bath. When the prepolymer filaments come into contact with the reactive solution, they polymerize creating an elastomeric thread.

[0041] The flow-rate of the stream of reactive mixture inside said tube 7 ranges from 30-60 m/min. At the end of the wet spinning phase, although the elastomeric polymer has been polymerized, it is still impregnated with polymerization solution, coming from the reactive bath. The separation of the reaction solution from the yarn is effected at the outlet of the tube 7 by free fall inside a collection container 8 situated below the free end of the tube 7. The solution collected is then sent to a transfer collector 9 and is conveyed, according to an embdiment, by means of a pump, not shown in the figure, to a general storage container. The reactive solution is finally put back into circulation after periodically reintegrating the quantity of reactive substance (diamine) used up in the reaction with the prepolymer.

[0042] The elastomer filaments, at the outlet of the tube 7, are joined into a thread preferably following a horizontal, and subsequently upward, run which includes passage on one or more thread-guides.

[0043] With these passages, the filaments, joined to form a thread, are squeezed to remove the remaining reactive solution.

[0044] The thread is then conveniently transferred by a thread-guide to a pair of rolls 10 and 11 for the drying phase.

[0045] The main purpose of the drying phase is to eliminate the residues of solution remaining after the squeezing phase and, after suitable curing treatment, to induce chemical and physical modifications to the thread, which give elastic properties to the end-product.

[0046] The drying phase advantageously comprises a passage of the thread over the hot surfaces of a pair of rolls 10, 11, following a spiral path. For this reason, the cylinders should be out of the axis. Alternatively, it is possible to use a pair of smooth rolls with the same diameter, both heated (pair of godets) or one with a greater diameter heated, and one with a smaller diameter not heated (godet and separator roll) or a pair of grooved cylinders, with the same dimensions, both heated.

[0047] According to an embodiment, the rolls are grooved and can have one or more helicoidal elements and a varying groove pitch: a wide pitch at the beginning of the roll to facilitate the drafting of several threads and a narrower pitch to allow a greater number of coils and consequently a longer run.

[0048] In the drying phase of the thread, the dimensions of the rolls are in relation to the spinning rate which should allow a sufficient residence time for drying the thread and effecting the curing treatment of the thread. The upper operating temperature limit of said rolls is preferably about 240° C., over which the thread begins to deteriorate, whereas the lower limit depends on the residence times on the hot rolls and the possibility of drying the thread. The temperature of the drying rolls preferably ranges from 180 to 240° C.

[0049] During the drying phase of the filaments, the air is sucked up, by means of a suction system 14, in order to avoid the discharge of solvent vapours from the spinning machine into the environment. The air sucked up, containing solvent vapours, is sent to a separation plant of the solvent, for example by means of condensation and/or adsorption on activated carbon.

[0050] Following the drying phase, the thread is conveniently transferred from the drying rolls to a lubricating system for example of the contact cylinder 13 or nozzle type. At the end of the lubricating phase, the thread is wound by means of a conventional winding system to form bobbins 12.

[0051]FIG. 2 illustrates a spinning position, generally indicated with 20, which can be used in the process of the invention, comprising a feeding tube 21 of the prepolymer connected to a moveable die-holder 22 shown in two positions, the first while operating and the second, indicated as 22′, in a non-operating position. The die 23 is assembled at the head of the die-holder 22 and is immersed in a reactive bath containing a solution at 4% of ethylenediamine in toluene, contained in a reaction recipient 24. The die is connected by means of a joint 25 to a duct 26, or flow-tube, in which the thread passes in equicurrent to a stream of solution. The recipient 24 is fed with the reactive solution through an opening 27 connected to a feeding collector connected to a storage tank, fed with a recycled solution, suitably filtered and re-integrated, of ethylenediamine. The solution circulates inside the recipient 24 from the inlet 27 towards the duct 26 together with the thread. The polymerization of the, polymer, which advantageously flows at a similar rate to the stream of reaction solution, takes place during its passage in said duct 26. During the spinning phase, the die-holder 22 is situated near the mouth of the duct 26. The die-holder 22 is moveable and can therefore be inserted and removed, when necessary, from the recipient 24, for example to allow the changing of the die.

[0052] The stream of solution in the spinning head 25 is conveniently distributed circumferentially around the filaments of prepolymer leaving the die. The geometry of the spinning head and horizontal tube is preferably such that the prepolymer filaments are sucked up and transported by the stream of solution and flow at an equal rate inside the tube 26.

[0053] The height of the bath in the container 24 is conveniently regulated, by means of the collector 27, by a system of vases communicating with the general storage tank of the bath (not shown).

[0054] The subsequent FIG. 3 illustrates a view from above of the spinning section 20 shown in FIG. 2. Inside the recipient 24, there is a reaction bath in which four dies 23, 28, 29, 30 parallelly arranged, are immersed. Said dies are connected, on the one hand, with the respective moveable die-holders 22 in turn connected with flexible feeding tubes 21 of polymer and, on the other, to the dies 23. The spinning tubes 26 in which the reaction solution flows are also arranged parallelly to each other.

[0055] Contrary to the processes of the known art in which the spinning lines treat numerous threads on the same equipment, in the process of the invention according to the embodiment illustrated in FIG. 3, the spinning line consists of various spinning positions, operating in parallel and with independent functioning, each of which produces a limited number of threads. The occasional breakage of a thread, during the process of the invention, consequently does not jeopardize the spinning of many of the adjacent threads, as happens in the known processes, as each spinning position is not only separate and independent from the others but also has a limited number of threads, typically from 2 to 8, preferably 4, as illustrated.

[0056] The following examples are provided for purely illustrative purposes and should therefore in no way be considered as limiting the protective scope of the present invention, which is defined by the enclosed claims.

EXAMPLE 1

[0057] A spandex thread was spun with the wet method in a dynamic reactive bath, according to the invention, using a single spinning position.

[0058] Operating parameters:

[0059] Type of polymer: polyurethane-ester-urea

[0060] Dies with 6 holes with Ø 0.2 mm

[0061] Height of the liquid seal of the coagulation bath: 200 mm

[0062] Coagulation tubes: internal Ø 4 mm, length 400 mm

[0063] Flow-rate of the coagulation bath: 0.55 l/min for each thread

[0064] Flow-rate of the polymer: 288 g/h for each thread

[0065] Spinning rate (winding): 240 m/min

[0066] Peripheral rate of the drying rolls: 220 m/min

[0067] Temperature of the drying rolls: 220° C.

[0068] The thread obtained had the following characteristics:

[0069] Titer: 200 dtex f 6

[0070] Tensile strength: 1.1 g/dtex

[0071] Ultimate elongation: 650%

[0072] Titer regularity (CV%): 1%

EXAMPLE 2

[0073] Spinning procedure of a second spandex thread, according to the process of the invention. The process was effected using the following parameters:

[0074] Type of polymer: polyurethane-ester-urea

[0075] Dies with 15 holes with Ø 0.18 mm

[0076] Height of the liquid seal of the coagulation bath: 100 mm

[0077] Coagulation tube: internal Ø 5 mm, length 500 mm

[0078] Flow-rate of the coagulation bath: 0.7 l/min for each thread

[0079] Flow-rate of the polymer: 600 g/h for each thread

[0080] Spinning rate (winding): 200 m/min

[0081] Peripheral rate of the drying rolls: 190 m/min

[0082] Temperature of the drying rolls: 225° C.

[0083] A thread was obtained with the following characteristics:

[0084] Titer: 500 dtex f 15

[0085] Tensile strength: 1.02 g/dtex

[0086] Ultimate elongation: 680%

[0087] Titer regularity (CV%): 1.1% 

1. A wet spinning process of an elastomeric polymer, which comprises: a wet spinning phase in which a prepolymer is put in contact with a reactive solution to give a polymeric thread; a drying phase in which the solvent of the reactive solution is removed from the thread; a collection phase in which said thread is wound on winding devices; wherein, in the wet spinning phase, said reactive solution moves in the direction of the thread-run in order to considerably reduce the hydrodynamic friction between the thread and reactive bath.
 2. The process according to claim 1, wherein said reactive solution moves at a rate ranging from 15 to 80 m/min.
 3. The process according to claim 2, wherein said reactive solution moves at a rate ranging from 30 to 60 m/min.
 4. The process according to claim 1, wherein said reactive solution comprises a diamine in an organic solvent.
 5. The process according to claim 4, wherein said diamine is ethylenediamine and said organic solvent is toluene.
 6. The process according to claim 1, wherein said prepolymer is an elastomer selected from the group consisting of polyester-urethanes, polyether-urethanes, or polyether/polyester-urethanes and mixtures thereof.
 7. The process according to claim 1, wherein in said wet spinning phase the prepolymer is fed to a spinning position comprising one or more dies, immersed in a reactive bath, each connected with a duct in which the thread runs in equicurrent with a flow of reactive solution.
 8. The process according to claim 7, wherein said prepolymer is polymerized while flowing in equicurrent with said reactive solution.
 9. The process according to claim 1, wherein the spinning is effected in one or more spinning positions, each of which comprises from 2 to 8 dies immersed in the same reactive bath.
 10. The process according to claim 1, wherein the reactive solution is removed from the polymeric yarn before said dry or hot phase.
 11. The process according to claim 10, wherein the removal of said reactive solution comprises squeezing of the thread.
 12. The process according to claim 1, wherein said drying phase comprises thermal curing treatment of the thread for increasing its elastic properties.
 13. The process according to claim 1, wherein said drying phase is made under heating by the passage of one or more threads on the hot surfaces of rolls.
 14. The process according to claim 13, wherein said rolls comprise grooves in each of which a single thread passes.
 15. The process according to claim 1, wherein said drying phase takes place at a temperature ranging from 180-240° C.
 16. The process according to claim 1, wherein a dried thread is lubricated before the collection phase.
 17. Equipment for the wet spinning of an elastomeric polymer comprising a series of spinning positions operatively independent of each other, each of which includes one or more dies arranged inside a reactive bath container.
 18. The equipment according to claim 17, wherein in each reactive bath container there are from 2 to 8 dies parallelly arranged.
 19. The equipment according to claim 17, wherein each die is connected by means of a spinning head to a device for the running of a thread in equicurrent with a reactive solution.
 20. The equipment according to claim 17, further comprising a drying section of an elastomeric yarn equipped with a pair of smooth heatable cylinders for the passage of one or more threads. 